The present invention relates to a novel device and to a process for treating a liquid medium, which are intended to remove microorganisms such as algae, bacteria, viruses, etc., and/or which are intended to allow a supersaturation with salts in the liquid medium.
It is known to those skilled in the art that, depending on whether high-frequency or low-frequency ultrasound is used, different effects can be obtained on fluids. In order to obtain mechanical effects, low frequencies (generally between 16 and 100 kHz) are regularly used.
These mechanical effects, which are due to cavitation, make it possible, for example, to mix, emulsify and disperse heterogeneous substances, to degas the liquids, etc. These mechanical effects also create high shear effects in the liquids, which makes it possible, for example, to disrupt living cells present in this medium, to the point of rupturing the walls of cells of this type.
These same mechanical effects are also used to clean surfaces by the action of the microjets of liquid produced by the implosion of the cavitation bubbles. Similarly, the fact that various reactants can be mixed very efficiently is advantageously used to promote diffusion phenomena in various chemical reactions, especially heterogeneous reactions.
If high frequencies are used, generally of between 300 kHz and several MHz, the cavitation phenomena become relatively less energetic and the mechanical effects are more reduced than when low frequencies are used.
By applying high-frequency ultrasound to a liquid medium, the lifetime of the cavitation bubbles produced is greatly reduced, and chemical phenomena in a homogeneous phase take place, which are radically different from those observed when lower frequencies are applied.
One parameter which is specific to the use of high-frequency ultrasound is that, despite the low mechanical energy required to degas the solutions, the effect obtained is greater than when low-frequency ultrasound is applied, which itself requires more power.
It is known from different prior art documents that the use of ultrasound allows the detoxification of liquid media.
American patent U.S. Pat. No. 5,198,122 describes a process for detoxifying liquid and solid materials comprising various toxic organic compounds, which consists in adding to the medium a catalyst comprising a sodium borohydride or a lithium aluminium hydride to the said materials, which are then subjected to ultrasound so as to bring about cavitation in the mixture and to allow easier detoxification or extraction of the contaminating substances.
German patent application DE-4,407,564 describes a process for oxidizing organic substances or microorganisms, which is obtained by adding oxidizing agents (ozone) or phase-transfer catalysts.
Japanese patent application JP-930343777 (Marsima Aqua Syst. Corp.) describes a process and a purification installation for a water reservoir containing vegetable plankton. In the first reservoir of this installation, the vegetable plankton is inactivated using an ultrasound vibrator which induces cavitation in the water. The product of this treatment is then transferred into a second reservoir, in which predation of the inactivated vegetable plankton by animal plankton is promoted.
Similarly, it has been proposed in various documents (JP-900401407 (Ina Shokuhin Kogyo KK), JP-920035473 (Kubota Corp.), JP-920035472 (Kubota Corp.) and JP-920035896 (Kubota Corp.) to bring about the removal of organochlorine substances or to remove microorganisms by a cavitation phenomenon using ultrasound and injections of ozone, peroxides and/or catalysts.
Japanese patent application JP-820010627 (Hitachi Kiden Kogyo KK) describes a process for removing algal spores by a mechanical effect brought about by the use of high and low frequency ultrasound, inducing the sterilization and removal of the spores which become attached to plates and are then removed by the purifying effect of the low frequency ultrasound cavitation.
All of these previous examples use the mechanical effects of low frequency ultrasound.
It is known from the scientific publication by Pxc3xa9trier C. et al. (Journal of Physical Chemistry, No. 98, 10514-10520 (1994)) that the sonochemical degradation of phenols in aqueous solutions varies as a function of the ultrasound emission frequency. According to that document, the degree of sonochemical degradation is thought to be directly associated with the presence in the solution of free radicals such as, for example, Hxe2x88x92, xe2x88x92OH and HOOxe2x88x92, originating from the sonolysis of the water by ultrasound. According to that document, the production of these free radicals, in particular the xe2x88x92OH and xe2x88x92OOH radicals, is said to be greater by working with high frequency ultrasound emission.
As is seen in the illustrations in that document, the radicals produced by ultrasound induce a fluorescence whose distribution varies as a function of the conception and design of the apparatus, as well as of the ultrasound emission frequency. This fluorescence induced by the radicals produced by ultrasound is demonstrated by the addition of luminol to the aqueous composition.
However, that document does not in any way suggest that the oxidation phenomenon obtained by high frequency ultrasound could be used to attack microorganisms present in this aqueous medium and thus remove them.
American patent U.S. Pat. No. 2,717,874 describes a device for processing an aqueous medium comprising microorganisms, by adding chlorinated reagents. The said device comprises a bell (cell) which communicates with a reservoir of the aqueous medium to be treated, and contains a high frequency ultrasound emitter located at the base of the bell. In addition, the bell has a device for emitting air bubbles at the cone of the geyser.
Patent application WO 93/13674 describes a process for pasteurizing milk or milk-based products so as to remove a certain number of microorganisms such as bacteria, viruses, spores, etc. The device and the process described in that document are based on the use of the cavitation obtained at low frequencies and at high power during particularly long application times.
European patent application EP-A1-0,633,049 describes a process for treating a liquid by emitting an ultrasound field so as to separate the particles present in this liquid. That process uses high frequencies, which allow the separation of the micro-particles by standing-wave fields in which the position is modified by a phase or frequency variation, which entrains the particles which thus remain concentrated in nodes or antinodes. In the case of biological particles, this device makes it possible to create a bioreactor in which the solid particles of any nature remain confined in the ultrasound field, which allows filtration of the liquid medium. It should be pointed out that the device makes it possible to sterilize biological materials and to inactivate microorganisms.
American patent U.S. Pat. No. 4,961,860 describes a process for treating water, so as to remove the microorganisms present by means of ultrasound emission of low-frequency power. However, that device requires particularly large energy consumption in order to obtain a mechanical effect which removes the microorganisms.
The present invention is directed towards providing a device and a process which can neutralize, prevent the growth of and/or remove a certain number of undifferentiated animal cells, such as tumour cells and/or microorganisms, in particular algae, bacteria, viruses, etc., from a liquid medium in a simple and inexpensive manner, and which do not have the drawbacks of the prior art.
One specific aim of the present invention is to neutralize, prevent the growth of and/or remove the said undifferentiated cells or microorganisms, in particular algae, present in liquid media such as swimming-pool water, water towers, fishponds, aquariums or any other water reservoir, and by extension any industrial circuit, for example a cooling circuit, in which the quality of the water is particularly important, or physiological fluids such as blood or plasma, which can be extracted from and/or administered to man or animals.
The invention is also directed towards obtaining a device and a process which do not require the addition of additional chemical products needed to obtain the abovementioned effects in the media treated.
Another aim of the invention is to obtain a device and a process which do not consume much energy.
An additional aim of the present invention is to obtain a device and a process for treating a liquid medium with ultrasound without giving rise to a standing-field phenomenon.
A final aim of the present invention is to provide a device and a process for treating an aqueous medium, which makes it possible to supersaturate the liquid medium with salts, i.e. to obtain salt concentrations greater than the natural solubility of these salts in the aqueous medium.